Run Windows7 alongside XP or Vista

Ever considered trying out Windows7 (for free even) without losing your existing computer setup? Sounds too good to be true, don't it. Welcome to the world of Virtual computing..

Most computer users run a single Operating System (OS), which is usually some version of Microsoft Windows. However as a few technogeeks are aware, it is possible to run more than one OS on the same computer.

What this means is having more than one bootable partition so that when the system starts up, the user has the option of selecting from different operating systems, say XP or Vista. These are known as multi-boot systems and can be tricky to set up, especially without accidentally losing existing data on the hard disk. See Partitioning Theory for more information.

Another option is to use what is termed as a Virtual Machine. Simply put, this is software which runs a whole operating system inside a window of another operating system, just like it was just another application. For instance here is an example of Windows7 (the guest system) running inside a virtual machine, which is running on Windows XP (the host system).

The virtual machine software 'fools' the guest OS into thinking it is running on a normal system, by emulating the hardware, which is a pretty nifty thing to do. The user can jumpt into the VM and use it just as if it was a second PC. On some monitors, depending on driver support, it is even possible to run the guest OS full screen size so the host OS is no longer visible. Keyboard shortcuts allow switching between full screen and windowed views of the guest OS.

Virtual machines (VMs) have a number of advantages. A multiboot system only allows booting into one OS at a time, whereas a virtual machine is much easier to set up and allows the user to run one or even multiple guest operating systems at the same time. The only real caveat here is that each guest OS uses allocated system resources such as RAM and CPU (plus some hard disk space) which are then not available to the host operating system, while the VM is running.

The example in the screenshot above is a Windows7 Enterprise VM running under Windows XP on a 2GHz system with 2GB of RAM. The host system firstly boots normally to Windows XP and then Microsoft Virtual PC is used to run Windows7 as a guest OS.

The VM is configured to allocate 1GB of system RAM to the Windows7 VM, which means that this RAM is not available to the Windows XP host while Windows7 is running. On a system with a fast CPU and gigs of RAM, both operating systems can concievably run at the same time without noticing a performance drop in either system, depending on what you're doing.

Which VM?

The choice of virtual machine software under Windows is usually between Microsoft Virtual PC and VMWare. They are both free for non-commercial use. I have used both for a number of years with various operating system combinations. For instance here is Unix running inside VMWare under Windows 2000 Server from a few years ago. They both work in similar ways. I am currently using Virtual PC for testing Windows7.